An adjustable mattress system which incorporates a containment means is described in detail in U.S. Pat. No. 5,513,402 granted May 7, 1996 to the applicant of this application, Jack Schwartz. The specification of U.S. Pat. No. 5,513,402 is incorporated herewith by reference. A containment means in the present context of a multilayer mattress system is the system used to keep a vertical stack of foam mattress elements aligned in the vertical stack, or a pair of adjacent mattresses (including a pair of stacks of foam mattress elements) together at their side-by-side median or meeting line. In U.S. Pat. No. 5,513,402, the containment means comprises, in one embodiment, a foam peripheral edge member called a cradle. In another embodiment, a fitted sheet is used, and in yet another embodiment, straps are used to interconnect head and foot ends of individual foam mattress elements in the side-by-side stacks.
It has been found that any failure in the containment means is most likely to occur when a person rests or shifts his weight in the middle of a mattress, particularly at the median line dividing two sets of adjacent stacks of foam mattress elements. While the containment means disclosed in U.S. Pat. No. 5,513,402 succeed in substantially keeping the stacks of foam mattress elements together, any small separation of the side-by-side mattresses at the median line is noticeable and is to be avoided. As can be understood, the use of a fitted sheet or the use of straps at the head and foot of the median line will contain the mattress assembly, yet it has been found that the tendency to separate at the median line in the middle of the mattress where the greatest weight and pressure is placed remains. Therefore, a containment means which is highly resistant to separation at the median line or as a result of shifting of weight in the middle of the mattress is very desirable. One solution to contain side-by-side mattresses is disclosed in French Patent Publication 2 590 142 (May 1987) in which the upper surface of the side-by-side foam mattresses are attached together by a strip of fabric so that separation along the median line is prevented. It has been found that this type of solution reduces independence between the side-by-side mattresses which is undesirable.
Also disclosed in U.S. Pat. No. 5,513,402 is a containment means which includes a foam peripheral edge member including slits in which a mattress cover and bottom sheet can be tucked in. It has been found that such a system for securing bedding can result in the bedding becoming loose under certain more extreme conditions.